The 23-year-old pounced in the 19th minute after a howler by veteran keeper Marco Ballotta.

And Lazio's woes deepened when midfielder Massimo Mutarelli was sent off in injury time.

With just one win in eight games in the Italian capital, the pressure was on the Romans to deliver, and they must have thought their luck was in when Fiorentina's top scorers Christian Vieri and Adrian Mutu were left on the bench.

But Pazzini showed he is not to be ignored when, with the first chance of the game on 14 minutes, he drilled a low shot which Ballotta had to react smartly to keep out.

And five minutes later the Viola went ahead with a goal which Ballotta will not want to forget.

The keeper went to prevent defender Sanchez Cribari's header from going out for a corner, but instead deflected the ball into Pazzini's path.

And with an open goal begging the striker couldn't miss, notching his fourth goal of the season.

Pablo Osvaldo almost doubled Fiorentina's advantage in spectacular fashion on the half-hour mark, with an acrobatic bicycle-kick. It was a weak effort though and Ballotta saved it easily.

Five minutes later Lazio came close to drawing level as Christian Manfredini's stunning 30-yard shot flew inches over the bar.

And the Biancoceleste could count themselves unlucky not to have gone into the break on level terms.

In the 40th minute Tommaso Rocchi's cross into the box found Lionel Scaloni in a great position and the Fiorentina defence had to scramble to keep the ball out.

Lazio came out in the second half fighting.

But faced with a Fiorentina side who have the second best defensive record in Serie A and have conceded only one goal in four away matches, there were few chances for an equaliser.

Their best effort came on the hour mark.

Stephen Makinwa took advantage of a rare mistake in the Viola back four and fired a tantalising cross into the area, but no-one was there to take advantage of the opportunity.

Pazzini had a great chance in the 73rd minute to double his and Fiorentina's tally, but Ballotta atoned somewhat for his earlier error, tipping the striker's fierce effort over the crossbar.

And five minutes later Lazio almost equalised but Rocchi took too much time to control the ball and the Fiorentina defence cleared it before he had the chance to shoot.

Viola keeper Sebastien Frey has been one of the reasons Fiorentina have conceded so few goals this campaign and he showed why with a stunning save on 82 minutes.

Rocchi played a one-two with Cristian Ledesma, before firing a shot which Frey did incredibly well to keep out.

And there was worse to come for Lazio in stoppage time as Mutarelli was shown a second yellow card for dissent.

The result sees Fiorentina maintain their unbeaten start to the season and pushes the Viola up to second in the table ahead of Sunday's games.

Lazio are left nervously looking over their shoulder in 14th place.